1. Field of the Invention
The present invention relates generally to auditory prostheses and, more particularly, to pitch perception in an auditory prosthesis.
2. Related Art
Voice pitch information can play an important role in speech perception as it provides cues to linguistic features such as intonation (question—statement contrast) and word emphasis (Highnam, & Morris 1987; Nooteboom, 1997; Wells, Peppe, & Vance, 1995). Voice pitch information also may make a significant contribution to paralinguistic features such as speaker identification and the emotional state of the speaker (Abberton & Fourcin, 1978; Liberman, & Michaels, 1962) and segregation of concurrent speakers (Brokx, & Nooteboom, 1982).
Most importantly, voice pitch information is crucial for perception of tonal languages, such as Mandarin and Cantonese, where a change in fundamental voicing frequency within the same phonemic segment causes a change in lexical meaning (Lee et. al., 2002; Ciocca et. al., 2002; Barry & Blamey, 2002). Pitch information is also of importance to the appreciation of music wherein the fundamental frequency and its harmonics govern the pitch of the signal (Moore, 1995; McKay & McDermott, 1997; Pijl 1995).
Various speech processing strategies have been developed for processing sound signals for use in stimulating auditory prostheses, such as Cochlear™ prostheses and hearing aids. The multi-peak strategy (Seligman, Dowell, & Blarney, 1992; Skinner et. al., 1991) focused particularly on coding of aspects of speech, such as formants and the fundamental voicing frequency. For this strategy voice pitch information was predominantly coded in the electrical stimulation rate. Other conventional strategies relied more on general channelization of the sound signal, such as the Spectral Maxima Sound Processor (SMSP) strategy, which is described in greater detail in Australian Patent No. 657959 and U.S. Pat. No. 5,597,390, both of which are hereby incorporated by reference herein. For this strategy voice pitch information (for a voicing frequency below approximately 200 Hz) is generally coded in the envelope signals of each channel by amplitude modulation at a frequency equal to or related to the voicing frequency.